The present invention relates to apparatuses and methods to minimize the infiltration of liquids through hatchways, particularly utility manholes that provide entrance to subterranean chambers.
According to information available in the environmental protection industry, the source of at least 35 percent of the inflow to sewage or wastewater treatment plants is rainwater or other non-wastewater liquid that has infiltrated the collection system. Reducing the amount of infiltrating water will reduce the volume demands imposed on these wastewater treatment plants and, thereby, decrease operating costs. Some wastewater authorities do not provide their own treatment, but pipe their wastewater to other facilities for processing. These authorities are charged monthly by the gallon of liquid piped and would immediately benefit by reducing the amount of rainwater or other non-wastewater infiltration. Private wastewater plants can realize the same benefits.
Other industries maintain extensive networks of equipment and wiring beneath the ground, for utilities such as electric, gas, fiber optic, telephone and cable services. These companies also desire to reduce the amount of rainwater infiltration to their utility vaults and thus of time and costs required to maintain manholes and vaults in dry and well-ventilated condition.
Most of the infiltrating liquid enters the above-mentioned systems through pick holes in manhole covers, which are perforations made through the cover to facilitate its removal and replacement using a pick or other tool. Some water also may enter between the cover and frame, especially if the assembly has become loose or worn.
Known systems for minimizing unwanted liquid infiltration include a variety of mechanical sealing devices, intended to prevent liquids from entering by these routes while allowing any gases that may be present to vent to the atmosphere. It has proved difficult to achieve both of these goals in a manner that would be cost-effective, where a large number of entry points are involved.
A common approach is to insert a polypropylene or metal bucket between the cover and the interior of the frame to capture and retain the infiltrated liquids. When filled to capacity, these buckets are difficult to remove because they are below the street level and may weigh over 20 pounds. Some devices also provide pressure-relief valves to vent the gases that would otherwise accumulate within the manhole, but the presence of these valves makes it still more difficult to open and close the manholes. U.S. Pat. No. 4,067,659 to Campagna, Jr. et al. discloses a bucket-like structure comprising a circular supporting flange that rests on the internal flange of a manhole cover support frame. A valve-member incorporated into the bucket relieves excessive gas pressure in the space beneath the bucket. Similar devices are disclosed in U.S. Pat. No. 4,650,365 to Runnels, U.S. Pat. No. 4,919,564 to Neathery et al., U.S. Pat. No. 4,957,389 to Neathery, U.S. Pat. No. 5,591,200 to Barton, and U.S. Pat. No. 5,957,618 to Sims et al. The later inventions are focused toward protecting the valves from damage and making the buckets easier to install and remove from the manhole. A similar approach is disclosed in U.S. Pat. No. 4,305,679 to Modi, which discloses the use of a plurality of expanding braces to compress an impermeable flexible membrane against the interior of the manhole frame. The resulting structure captures water flowing through the manhole cover and blocks water from entering the manhole through the joints between the frame and the manhole chimney. The braces must be compressed and removed from the frame to gain entry to the manhole.
Another approach is to install a closure plate to block the inflow of water. The use of a plate in place of a bucket reduces the amount of water collected beneath the cover. These devices typically include pressure relief valves to vent gases accumulating beneath the cover plate. The cover plates are designed to rest on an integral flange within the manhole frame. If no flange is present, a retaining ring or other suitable support structure must be installed. Devices of this type are disclosed in U.S. Pat. Nos. 3,712,009 and 3,798,848 to Campagna, U.S. Pat. No. 3,969,847 to Campagna et al., U.S. Pat. No. 3,973,856 to Gaglioti, and U.S. Pat. Nos. 4,030,851 and 4,512,492 to Graybeal.
Another approach is to provide an elastomeric seal between the contact surfaces of the cover and frame. The holes in the cover are filled to minimize infiltration or a cover without holes is used. The seal may be held in place by the weight of the cover or bolted securely to the frame. The main drawback of sealing the manhole in this manner is that the gases within the manhole chimney do not vent to the atmosphere and, therefore, may accumulate to hazardous levels. It is also more difficult to open and reseal the access opening. U.S. Pat. No. 4,763,449 to Vigneron et al. provides an elastomeric sealing ring interposed between the cover and an integral flange within the frame. A plurality of bolts and movable flanges recessed within the frame are used to hold the cover firmly against the sealing ring. These bolts and flanges must be loosened or removed to gain entry to the manhole. U.S. Pat. No. 4,934,715 to Johnson discloses the use of an elastomeric gasket to form a water-tight seal between a cover and frame. The circular groove must be formed within the frame to receive the gasket. The gasket is squeezed between the frame and cover using a plurality of bolts. U.S. Pat. No. 4,101,236 to Meyer provides a manhole cover with an O-ring groove and no perforations. The O-ring groove is positioned to allow an elastomeric O-ring to form a seal between the cover and the contact surface of a conventional manhole frame. U.S. Pat. No. 4,440,407 to Gagas discloses the use of an L-shaped elastomeric gasket to provide a seal between the contact surfaces of a manhole cover and frame. U.S. Pat. No. 4,597,692 to Gruenwald discloses the use of elastomeric gaskets and plugs to minimize inflow of water by forming a seal along the perimeter of the manhole cover and closing the perforations within the cover.
The present invention disclosed herein addresses the drawbacks of known devices and methods. One aspect of the present invention provides venting structures that utilize liquid-repellent, gas-permeable membranes to capture liquids that infiltrate manhole covers, while allowing gases to pass through the membranes. Certain preferred assemblies will also be useful to prevent particulate solids, such as sand or dirt, from penetrating between the cover and frame and causing them to bind together. The preferred assemblies are light-weight and simple to install and can be fabricated from materials that are widely available. The most preferred assemblies can be modified to accommodate field conditions.
In accordance with one embodiment of the present invention, there is provided an assembly that minimizes the infiltration of liquids into a manhole or other hatchway. The assembly comprises a venting structure that is installed between the manhole cover and frame. The venting structure, most preferably, utilizes a water-repellent gas-permeable fabric to contain or divert liquids that would otherwise enter the manhole through openings in the cover or between the cover and frame. The fabric allows gases and vapors that may exist in the manhole chimney to vent to the atmosphere.
In a preferred embodiment of the present invention, the assembly comprises a cover support frame; a sheet of water-repellent gas-permeable material covering the central opening of the support frame and preferably folded over a stiffening ring; and a cover mated to the frame. More preferably, additional sealing materials and/or packing elements are used to minimize movement of the cover in the frame and provide a non-wearing surface for the sheet of material, and to improve the liquid-tight seal between the cover and flange.
In another embodiment, the invention provides a venting structure for minimizing the infiltration of liquid into an access opening, such as a manhole or hatchway, while allowing gases to escape through the access opening. The venting structure comprises a sheet of liquid-repellent, gas-permeable membrane adapted to substantially occlude an opening in the venting structure. Preferably, the venting structure is adapted to be installed between the cover and the support frame that defines the access opening. The sheet may be adapted by cutting and folding portions of the sheet over a stiffening ring to provide structural support. The sheet may also be adapted by fluting its edges to form a dish-like structure conforming to the perimeter and underside of a provided cover.
In accordance with another aspect of the present invention, there is provided a method for minimizing infiltration of liquids into an access opening while allowing gases to escape through the access opening. Preferably, the method includes cleaning the surfaces of the frame and cover to remove dirt and other abrasive material; placing a venting structure over the access opening, partially overlapping the frame; and lowering the cover into place so that the venting structure is held in place between the cover and frame. More preferably, the method includes inspection of the assembly to determine that the cover is securely seated against the frame so that it does not move under normal traffic conditions and, if the frame is installed in the ground, that the cover is level with the top of the frame and grade. Most preferably, if the assembly is unsatisfactory, the method includes disassembling the assembly and providing a sealing element or packing material is placed along the rim of the frame to improve the fit between the cover and frame. Most preferably, the assembly process and inspection are repeated until the cover is securely seated against the frame.